1. Field of the Invention
The present invention relates to a manufacturing method of a polarizing film. An obtained polarizing film may form a visual display, such as a liquid crystal display, organic EL display, and PDP, as an independent film itself or as an optical film laminated thereof.
2. Description of the Prior Art
In a liquid crystal display, based on a display formation method, it is indispensable to configure a polarizer at both sides of a glass substrate, which forms a top face of a liquid crystal panel. Generally, a polarizing film is used in which a protective film is adhered onto a polarizer comprising a polyvinyl alcohol derived film and dichroism substances, such as iodine.
Conventionally the polarizing film is manufactured by laminating a polarizer onto a protective film by adhesives. Adhesives are compounds or compositions that have a binding component, and these are used also as a solution dissolved in water or in organic solvents and also are cured by heating, light irradiation or chemical reaction, etc. Immediately before a polarizer and a protective film are adhered together these adhesives are poured in between these layers, or they are beforehand applied on either a polarizer or a protective film.
However, when adhesives are used, several manufacturing processes are required, such as a coating process, a laminating process, and a drying process and as a result a large amount of expense is needed for a production equipment. Furthermore a saponification processing, a corona processing, a plasma processing, or a low-voltage UV processing, further an undercoating processing is required to be applied onto a protective film, in order to raise an adhesive property with a polarizer. Consequently, a production cost of the polarizing film obtained also becomes expensive. Moreover, if a manufacturing process is constituted by many processes, a factor generating defects in each of the processes will also be increased.
And moreover, since many types of water-soluble adhesives, such as a polyvinyl alcohol aqueous solution, are used as said adhesives, the polarizing film manufactured fails to have a sufficient durability under heated and humidified conditions. Therefore, an adhesives portion of tends to be affected by moisture and this fault is one of causes of early degradation of a polarizing film.
An object of the present invention, therefore, is providing a manufacturing method of a polarizing film in which problems caused by using adhesives are solved. And an object of the present invention is providing a polarizing film, furthermore an optical film.